Grow Beds in Home Aquaponics System

The GROW BED is the multi function centre of the Home Aquaponics System.

The Grow Bed performs several very important tasks, and if we were to try and describe those functions in a simple way, one suitable description would be, it is a Bio-Filter in which we grow plants.
A very happy and combination of duties. It is extremely convenient for our purposes, because as a Bio-Filter it collects and processes the ammonia and solid waste from the fish and returns the water to the fish tank clean, and by the growing of plants in the Bio-Filter (Grow Bed) we use up the nutrients and nitrates produced in the Bio-Filter (Grow Bed) producing excellent quality fresh veggies for our table.

Because the Grow Bed is such an important part of our total Aquaponics System we need to put some careful thought into it's design. Materials used, dimensions and location relative to the fish tank are all considerations.
We strongly recommend the use of 300mm (one foot) deep grow beds in your Aquaponics system. Beds with less depth and therefore volume, will also work, but not nearly as well.

The Grow Bed needs to be of such a length and breadth to provide sufficient surface area for the plants and together with depth provide sufficient total volume to be an effective Bio Filter.
Overall volume of a grow bed is an important factor. The more volume the total system has, the more stability in the system , particularly in temperature and pH.

This stability has obvious flow on benefits for the health of the system inhabitants.

Fish, plants, worms, beneficial bacteria and microbes all function better in a stable environment.

In taking the decision to operate an Aquaponics system, we are desirous of producing the very best, healthy, nutrient rich and economical, plant and protein, for our family.
Aquaponics can deliver such produce by making use of natures wonderful interactive systems of worms, microbes and bacterium in a naturally balanced environment. It all works to its optimum when we provide it the best environment possible.

300mm (or more) deep grow beds will deliver optimum plant growth and health. They will provide optimum environment for the processing and delivery of nutrients to the plants, and the processing conversion of the ammonia given off by the fish, to nitrates.

In forming this opinion we have relied, not only on our own actual, very significant practical experience, but also on the experience of dozens of very experienced AP practitioners in Australia and around the world. Many of these people have accumulated a large body of experience in the use of 300mm deep (or deeper) grow beds as part of a well constructed Aquaponics system.

All of these people report exceptional healthy plant and fish growth using systems based on the 300mm deep grow bed principle. There is now a large body of actual evidence that strongly shows that this is a good working principle/method.

We have manufactured and delivered many hundreds of complete AP kits based on the 300mm deep grow bed, and hundreds of 300mm deep grow beds to persons who are constructing DIY Aquaponics systems.

Flood and Drain:
Together with a 300mm (one foot) grow bed depth, we strongly recommend using flood and drain cycle and 20mm drainage gravel or similar in your grow beds.
Flood and drain water movement system ensures the even distribution of water, nutrients and air (oxygen) throughout the system. This provides multiple benefits.
By the use of this method, dry or nutrient and oxygen areas are prevented from forming in the grow bed.

Nothing less than 20mm (3/4”) gravel should be used. This common gravel, by the way it rests together provides easy passage of water, solids, and worms throughout the bed.

Often folk cannot envisage plants growing in such a coarse media and they choose a finer media such as 5 or 10mm. This sized media will impede the action of the worms, the easy movement of solids and nutrients, and the Grow Bed will quickly suffer from partial or complete blockages.
Listed below are some of the reasons why 300mm or deeper grow beds are good....very, very good and highly recommended to deliver excellent results in your Aquaponics System.

Room for plant roots to develop and grow.
Some plant types such as lettuce do not require much depth (or nutrient) to grow successfully, but other garden plants such as tomato and corn, just to name two more common ones, do need depth space to put down good root systems. A given grow bed will have a variety of plants grown in it, so a grow bed depth bed depth that will accommodate a wide range of plant requirements is the way to go.

Depth and volume to process solid waste.

Solids passed by the fish, old roots, and other solid material is processed in the grow beds by those little wonder worms. Without going into detail here about the role of worms in AP, sufficient to say that the worms reduce solid waste by 60% or more and by their work and the action of flood and drain distribute the released minerals and nutrients throughout the grow bed/s.   300mm deep grow beds filled with 20mm drainage gravel with a good population of resident worms deliver an amazing plant growing habitat. (Not to mention excellent filtration for the fish tank.)

Bed Zones are established. (See attached illustration

Surface or dry zone. --- # 1. The first 50mm is the light penetration and dry zone. Evaporation from the bed is minimised by the existence of a dry zone. Water waste minimisation is a very important principle in Aquaponics systems.

This dry zone also protects the plant base against collar rot. Additionally, by ensuring that this zone is kept dry, algae is prevented from forming on the surface of the grow bed media. Because this dry zone is present, moisture related plant diseases such as powdery mildew are minimised.

Root zone. --- # 2.  Most root growth and plant activity will occur in the next zone of approximately 150 - 200mm –in this zone, during the drain part of the flood and drain cycle, the water drains away completely, allowing for excellent and very efficient delivery of oxygen rich air to the roots, beneficial bacteria, soil microbes, and the resident earth/composting worms.

During the flood part of the cycle, the incoming water distributes moisture, nutrients and incoming solid fish waste particles throughout the growing zone. The worm population does most of its very important work in this zone, breaking down and reducing solid matter and thereby releasing nutrients and minerals to the system. ?Worm Tea”, as it is commonly known, will be evenly mixed and distributed during each flood and drain cycle. “Worm Tea” and the fish are entirely compatible, No possible harm can come to the fish by the distribution of this wonderful nutrient material throughout the Aquaponics System.

Solid collection and Mineralisation Zone - # 3.
This is the bottom 50plus mm of the grow bed.   In this zone fish waste solids and worm castings are finally collected.

The solid material has been reduced by up to 60% by volume, by the action of the resident garden/composting worms, and microbial action.
During each flood and drain cycle, what is left of the solids perkolates down into this zone
Further and final mineralisation occurs in this area via bacterial and earth worm activity. Due to the excellent action of the flood and drain cycle, this bottom area is kept “fresh” and vital by the excellent delivery of oxygen rich water during the flood cycle.

Some water storage occurs in this bottom zone.
Should the flood and drain cycle stop for any reason, such as a mains power outage, the bed will slowly drain down and leave approx 50mm of water at the bottom of the grow bed.
The stored water provides a safety buffer in the event of power outage or pump failure... This stored water ensures that the plants will survive for very long periods without water flow.

This means that we can simplify our safety backup system to circulate only the water in the fish tank, by the use of low wattage water pumps and/or aerators.  We can safely operate the system in backup mode (no main power supply) for very long periods of time–simply using an average size car battery as a power source.

This inbuilt water storage zone will supply the plants with water and nutrient should we need to isolate the fish tank for maintenance purposes, or treatment of the fish.

Happy Aquaponics

Murray Hallam.

14 Responses to Grow Beds in Home Aquaponics System

  1. shea says:

    Hi Murry,
    Given the area that I am in, I have about 6 to 7 hours of direct sunlight for my planting beds. Is that enough light given the common types of veggies such as tomatos, lettuce, corn, etc?


  2. Murray says:

    I see by your IP address that you are in Florida so you will be coming into summer and I assume that the 6 or 7 hours you are talking about is winter sun. You can grow most if not all veggies (in season) that normally grow in your area.
    I hope this helps.

  3. Stephen says:

    Hi Murray, firstly, awesome site for information, thank you. Second, is algae in aquaponics a good thing? The research I have done is leaning towards yes, can you clarify this please. Cheers Murray.

  4. Murray says:

    Hi Stephen,
    A little is ok, in fact it is hard to avoid have some in your AP system. Algae is part of the overall ECO system. Too much can become a problem robbing the system of oxygen and nutrient. Keep direct sunlight away from the water and it is usually not too much of a problem.

  5. Andrew Martin says:

    Hi Murray,
    I am really new to the ap idea and am buying a 1000lt industrial tank and going to build one this weekend, could you give me any lists of materials including pumps etc. and websites I should look at. I realise one this size wont yeild that much but want to give it a test run so when I buy a house I can set up something decent. Also I’m thinking of Barra or Murray Cod for the fish, are they easy and hardy enough?any advice would be great. I really enjoyed your you tube video’s and am getting your dvd, Think I may have found a new passion haha.
    Andrew 0414504630

  6. Murray says:

    The DVD,s are a good place to start your quest for knowledge. I look forward to seeing your progress.

  7. Dustin says:

    Hi Murry,
    Thanks for all the information, you are truly changing the world. I live in Austin, TX and we have quite bit of limestone in the area. 3/4″ limestone gravel is readily available but should I use it? Will it effect ph?

  8. Murray says:

    Hi Dustin, Limestone in the gravel will effect the pH of the system and is therefore not desirable. It may be a bit difficult for you, but you need to source some sort of media that is pH neutral.

  9. traci says:

    Hi Murray,
    Terrific information! so totally helpful to us newbies. We have a 300 gallon tank with 7 adult tilaps and about 60 1″+ babies. We have 4 grow beds, 2 are filled with cinder and 2 are our experiment of using hydroponic pots and placing them in the grow beds, instead of filling the beds up completely. The 2 with the pots are doing really well but there is a lot of algae in the grow beds because of the exposure to sun. We are now getting a lot of algae in the fish tank now that the babies are getting bigger. Is the algae ok in the growbeds? How should we reduce the algae in the fish tank?
    Mahalo for your knowledge and help!

  10. Murray says:

    It is a good idea not to expose the water to direct sunlight. Direct sunlight on the nutrient rich water will produce algae. Tilapia , as I understand it should consume some of the algae from the tank sides, so long as there is not too much of it. Shield the water from direct sunlight will help heaps. That may require a cover over the fish tank and filling the beds above the flood level.

  11. Evie DeChant says:

    Hi Murray
    First I want to tell you how thrilled I am about the AP system… it is like a marriage of my 2 most favorite passions.
    I Live in Georgia and was wondering if you could tell me what type of PH neutral gravel media I could look for here?

  12. Murray says:

    Hi Evie,
    Look for a basalt type crushed rock gravel or river stone. 3/4″ is ideal. Make sure there is no limestone or other compounds in the gravel mix that may push the pH upwards. You can test this by getting a bucket of the intended gravel carefully measure the pH of your water then put water into the bucket of gravel, test the pH of the water in the bucket a few days later. In any case, the gravel supplier should be able to tell you if there is limestone in the gravel mix.

  13. Tim says:

    Hello Murray,

    Building my first system out here in sunny Southern California. Do you see a problem with mixing the clay pebbles with gravel? I am using a single IBC tote for the system, can this system handle an additional grow bed?


  14. Murray says:

    Hi Tim,
    It is often done, mixing the two. Usually the top 4 inches in clay pebbles and the course gravel in the bottom of the bed. After a while you will find that they get mixed together, as you pull finished plants the gravel tends to come up towards the surface. I am sureit will work well for you.

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